1. Field of the Invention
The invention relates to a valve rotating mechanism for exhaust valves, especially of marine diesel engines or the like, which mechanism is braced in a valve housing for the valve stem between an upper and a lower drive element, wherein it is linked to the lower drive element via a freewheel device, which allows rotation of the valve stem during closing movement thereof, and wherein it is braced relative to the upper drive element via a rotary cylinder, which brings about rotation of the valve stem through engagement with a fixed support cylinder.
2. Description of the Related Art
Such a valve rotating mechanism is described in German Patent 3113944. The known mechanism comprises two cylindrical portions, which are disposed concentrically relative to one another and between which two balls are guided in rotational movement in such a way that they respectively engage in a ball socket of the one cylindrical portion and in a ball track of the other cylindrical portion, the said track running at an inclination to the cylinder axis. A more uniform distribution of force between the two cylindrical portions is achieved by providing a plurality of ball sockets and ball tracks disposed at intervals around the circumference of the two cylindrical portions. Preferably the ball tracks have the form of a spiral with constant pitch.
In this known valve rotating device, a cylindrical portion is rotated by the fact that the ball guided in the ball socket travels in the ball track of the other cylindrical portion, one of the cylindrical portions being locked by the freewheel device. During closing of the valve stem, the cylindrical portion locked during opening is driven in the direction of rotation.
By means of the known mechanism, a relatively high speed of rotation of the valve stem can be attained during the closing operation; however, some wear of the ball tracks has to be expected, meaning that regular replacement of the corresponding cylindrical portions is inevitable.